Current and future emissions requirements for diesel and gasoline engines in Europe, US and most foreign markets will require engine concepts capable of achieving low NOx and low particulate matter emissions while at the same time meeting requirements for low-cost systems and packaging needs.
FIG. 1 is a schematic illustration of a prior art diesel engine breathing system 64 using a single-stage turbo charger. Such a system 64 includes a low pressure exhaust gas recirculation (EGR) loop 66, including a first EGR path 7, a first EGR valve 8, and a first cooler 9.
The system 64 includes a high-pressure loop 68 having a second EGR path 15, second EGR valve 16 and second EGR cooler 17. Exhaust gas is generated by an engine 1 and exits through an exhaust gas manifold 2. The exhaust gas from the exhaust gas manifold 2 can be directed in two directions.
In the first direction, the gas may flow through the high-pressure loop 68 and into the intake manifold 14. To create enough EGR flow through the second EGR path 15 and second EGR cooler 17, the second EGR valve 16 can be adjusted accordingly. If the second EGR valve 16 is fully opened and more flow through the second EGR path 15 and second EGR cooler 17 is required, the intake first throttle valve 13, which is commonly a flapper-type valve, can be closed gradually.
Alternatively, in the second direction, the exhaust may pass through the variable turbine 3 and be introduced into a diesel particulate filter 4, where the gas may be cleaned of various constituents that may include soot, carbon monoxide or hydrocarbons. After flowing through the diesel particulate filter 4 and the exhaust throttle 5 the exhaust gas then exits through the exhaust pipe 6. The first EGR valve 8 can be opened to allow flow through the low-pressure loop 66 to the intake duct 10 and toward the compressor 11 of the turbocharger. Along this second direction, particulates may collect on the diesel particulate filter 4, which may release small particulates that flow through the EGR path 7 to the compressor 11. The particulates may form resin-like deposits of unburned hydrocarbons on the compressor blades. In addition, condensate or droplets from the exhaust gases may flow through the EGR path 7 to the compressor 11.